1. Field of the Invention
The present invention relates to a window attached to a process chamber and, more particularly, to a quartz window attached to a process chamber for applying a thermal process to a substrate placed inside the process chamber by applying a heat through the quartz window.
The present invention is especially suitable for a window provided to a rapid thermal processing (RTP) apparatus, which is preferably used for a manufacturing process of semiconductor devices such as a memory device or an integrated circuit (IC). The RTP includes a rapid thermal annealing (RTA), a rapid thermal cleaning (RTC), a rapid thermal chemical vapor deposition (RTCVD), a rapid thermal oxidation (RTO), a rapid thermal nitriding (RTN), etc.
2. Description of the Related Art
Generally, in a manufacturing process of a semiconductor integrated circuit, a semiconductor substrate such as a silicon wafer is repeatedly subject to various thermal processes or heat treatment processes. The thermal processes may include a film deposition process, an annealing process, an oxidation diffusion process, a sputtering process, an etching process, a nitriding process, etc.
In order to improve a yield rate and a quality of semiconductor products, the RTP technique, which rapidly increases and decreases a temperature of an object to be processed, has attracted a great attention. A conventional RTP apparatus generally comprises: a single-wafer process chamber in which an object to be processed, such as a semiconductor wafer, a glass substrate for photo-masking, a glass substrate for liquid-crystal display or a substrate for an optical disk, is placed; a quartz-glass window attached to the process chamber; a heating lamp such as a halogen lamp; and a reflector provided on an opposite side of the object to be processed with respect to the heating lamp. Hereinafter, the object to be processed may be referred to as a target object.
The quartz-glass window is formed in a platelike shape or in a tubular shape in which the target object can be accommodated. When gasses inside the process chamber are evacuated by a vacuum pump and a negative pressure environment is maintained in the process chamber, the quartz window has a thickness of about 30 mm to 40 mm so as to withstand with a pressure difference between inside the process chamber and an atmospheric pressure. The quartz-glass window may have a concave shape so that the center thereof is apart from the process space inside the process chamber since the quartz window tends to be bent toward the processing space due to a temperature increase.
A plurality of halogen lamps is arranged so as to evenly heat the target object, and the reflector uniformly reflects an infrared light toward the target object. The process chamber is typically provided with a gate valve on a sidewall thereof so as to let the target object transported therethrough. Additionally, a gas supply nozzle is connected to the sidewall of the process chamber so as to introduce a process gas used for a thermal processing.
Since the temperature of the target object influences a quality of the process (for example, a thickness of a deposited film in a film deposition process), the temperature must be accurately detected. In order to achieve a rapid temperature increase or decrease, a temperature-measuring device is provided in the process chamber so as to measure the temperature of the target object. The temperature-measuring device may be comprised of a thermocouple. However, the thermocouple may contaminate the target object due to a metal constituting the thermocouple since the thermocouple must be brought into contact with the target object.
Accordingly, a pyrometer has been suggested, such as disclosed in Japanese Laid-Open Patent Application No. 11-258051, as a temperature-measuring device for measuring a temperature of the target object. The pyrometer calculates a temperature of the target object by converting an emissivity xcex5 into a temperature, the emissivity xcex5 being calculated by the following equation (1) based on an intensity of radiation of infrared light radiated from a back surface of the target object.
Em(T)=xcex5EBB(T)xe2x80x83xe2x80x83(1)
In equation (1), EBB(T) represents an intensity of radiation from a black body having a temperature T, Em(T) represents an intensity of radiation from a target object, and xcex5 represents an emissivity of the target object.
In operation, the target object is introduced into the process chamber through the gate valve, and supported by a holder on its periphery. During a thermal process, a process gas such as nitrogen or oxygen is introduced into the process chamber through gas supply nozzles. On the other hand, the target object absorbs an infrared light radiated by the halogen lamp, thereby increasing the temperature of the target object. An output of the halogen lamp is feedback-controlled in accordance with a result of measurement of the temperature-measuring device.
However, the conventional quartz window has a thickness as large as several millimeters, there are following problems. First, the light emitted by the lamp is absorbed by the quartz, which results in a decrease in an efficiency of irradiation of the target object. Second, The quartz window easily breaks due to a difference in thermal stress between front and back surfaces of the quartz window when a rapid temperature increase is performed such as in the RTP apparatus since a temperature difference is generated between the lamp facing surface and an opposite surface of the quartz window. Third, if the quartz window is bent, a distance between the lamp and the target object is increased, which deteriorates directivity of the irradiation by the lamp. Fourth, especially when a film deposition process is performed, a deposition film or a reaction by-product may deposit on the surface of the quartz window due to an increase in the temperature of the quartz window, which may deteriorate reproducibility of a process temperature and increase a frequency of cleaning operations of the process chamber. On the other hand, if the thickness of the process chamber is reduced, absorption of the light radiated from the lamp by the quartz window can be reduced.
However, there is a problem in that the quartz window is easily broken due to a difference between a negative pressure in the process chamber and an atmospheric pressure and, thereby, such a quartz window cannot applied to the process chamber in which a negative pressure environment is created.
It is a general object of the present invention to provide an improved and useful quartz window in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a quartz window, which can withstand a pressure difference between an atmospheric pressure and a negative pressure environment created in a thermal processing apparatus that applies a thermal process to a target object under the negative pressure environment.
Another object of the present invention is to provide a quartz window, which absorbs a relatively small amount of heat radiated from a heat source.
In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention a quartz window of a process chamber adapted to be positioned between a radiation heat source and an object to be subjected to a heat treatment in the process chamber, the quartz window comprising: a plate made of quartz; and a plurality of ribs formed on the plate so as to reinforce the plate.
According to the above-mentioned invention, the plate of the quartz window has a reduced thickness since the ribs reinforce the plate. Thus, the overall thickness of the quartz plate is reduced, which improves the directivity of heat supply by the radiation heat source to the object to be processed. Additionally, an amount of heat absorbed by the quartz window is reduced.
In the quartz window according to the present invention, the ribs may be made of quartz, and the ribs may be integrally formed with the plate. In one embodiment, the ribs may include a plurality of radial ribs extending in radial directions of the plate. The radial ribs may be symmetrically arranged with respect to the center of the plate. Additionally, the ribs may include a plurality of circumferential ribs extending in circumferential directions of the plate. The circumferential ribs may be concentrically arranged.
The plate of the quartz window preferably has a thickness equal to or smaller than 10 mm. Each of the ribs preferably has a thickness equal to or less than 10 mm and a height equal to or less than 15 mm.
The ribs may have openings to let air pass therethrough.
Additionally, there is provided according to another aspect of the present invention a thermal processing apparatus comprising: a process chamber in which an object to be processed is placed; an exhaust part connected to the process chamber so as to evacuate gas inside the process chamber; radiation heat sources which apply heat to the object placed in the process chamber; and a quartz window situated between the radiation heat source and the object, wherein the quartz window has a plurality of ribs formed on a quartz plate so as to reinforce the quartz plate.
According to the above-mentioned invention, the plate of the quartz window has a reduced thickness since the ribs reinforce the plate. Thus, the overall thickness of the quartz plate is reduced, which improves the directivity of heat supply by the radiation heat source to the object to be processed. Additionally, an amount of heat absorbed by the quartz window is reduced.
In the thermal processing apparatus according to the present invention, the ribs may be made of quartz, and the ribs may be integrally formed with the plate. In one embodiment, the ribs may include a plurality of radial ribs extending in radial directions of the plate, and the radial ribs may be symmetrically arranged with respect to the center of the plate. Additionally, the ribs may include a plurality of circumferential ribs extending in circumferential directions of the plate, and the circumferential ribs may be concentrically arranged.
Additionally, the thermal processing apparatus according to the present invention may further comprise a reflector which reflects a heat radiated from the radiation heat source toward the object through the quartz window, and the reflector has accommodating parts accommodating the radiation heat source and a plurality of extending parts extending toward the plate of the quartz window, the extending parts being engaged with the respective ribs of the quartz window.
Since the reflector has grooves that receive the respective ribs of the quartz window, the overall thickness of the structure including the quartz window and the reflector is reduced, which reduced a distance between the radiation heat source and the object to be processed. Additionally, the ribs of the quartz window engage with the inner walls of the grooves when the quartz window is bent due to a pressure difference caused by a vacuum created in the process chamber. Thereby, the quartz window is prevented from being further deformed, which further reduces the thickness of the quartz window.
In one embodiment, each of the extending parts may have a groove which receives a respective one of the ribs of the quartz window. Each of the ribs may protrude into a respective one of the accommodating parts so that each of the extending parts of the reflector is positioned between adjacent ones of the ribs.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.